Background: The circle of Willis is an anastomotic network of arteries surrounding the base of the brain. People with effective collateral circulation will lower the risk of transient ischemic attack and stroke than those with ineffective collaterals. Objectives: The research aims to study the diameter of arteries and determine the frequency and patterns of anatomical variations in Vietnamese patients' anterior and posterior parts of the Willis polygon. Methods: This descriptive cross-sectional study was conducted in Vietnam at Bach Mai hospital between July 2010 and July 2011. A total of 102 MSCT 64 examinations were conducted on adult patients with suspected cerebrovascular diseases such as stroke, cerebral infarction, etc. The average internal diameter of arteries was estimated using descriptive statistics. Wilcoxon signed-rank test paired t-test to compare diameter on the left and right sides. Results: There are four types of anterior parts and twelve types of posterior parts in the circle of Willis. Of the 102 subjects, 29.41% experienced the anterior part of circle of Willis (CoW), in which aplastic anterior communicating artery (ACoA) is the most common type (21.57%). 70.59% of all subjects have variations in the posterior part of CoW, and bilateral aplastic posterior communicating artery (PCoA) is the most common type (20.59%). We also report the diameter of cerebral artery segments of the circle of Willis. There are six variations in the circle of Willis based on the correlation between pre communicating part P1 of posterior cerebral artery (PCA) (P1) and PCoA diameter. The most popular type is adult configuration (53.92%). Conclusions: We provided the prevalence and the pattern of the brain vascular variants of the circle of Willis in a group of patients diagnosed with ischemic stroke. Understanding the variations and diameter of the circle of Willis is of great importance in interventional radiology for various endovascular interventions in Vietnamese patients.